I recommend 27 GAL Lowes yellow top totes for doubles and singles they average $5-9 bucks a pop but are well worth the investment. if you can find the link or know someone with a 3d printer they can make you these pocket inserts that use PVC to support across to stack the modules if your top modules are shallow enough. I like them alot especially for basement storage
The problem I run into with this approach (which I took for a while) is that it's very space inefficient. It's great for a single module, or maybe two, but when you've got a whole fleet those extra few inches on each end due to the lips and the mis-match between the module dimensions and interior dimensions eat up a LOT of valuable transport space.
It's why I'm a huge fan of plywood coffins or end plates for married pairs.
And when you're designing said enclosures make sure to think of the entire workflow of crating, carrying, carting, and opening them. For example, if you have a tall building, make sure that not only does the top of the lid clear it when things are bolted in, but ALSO make sure that it clears it when you set the thing on the table with the leg bolts extended. You don't want your box smashing something while you're in the process of boxing it up. Yes, you can "be careful", but it only takes
one "packing up in a hurry before the snow starts" show to get you into trouble.
